1. Field of the Invention
The present invention relates generally to a flare stack, and more particularly, but not by way of limitation, to a flare stack adapted to heat incoming fuel, such as off-gases, and optionally, to heat a secondary fluid, such as glycol.
2. Brief Description of Related Art
A number of systems exist for dehydrating natural gas to remove water and other liquids from natural gas. Most of these dehydration systems involve passing the natural gas through or in contact with one of a number of known desiccant fluids, such as glycol. For brevity, the desiccant fluid may hereinafter be referred to as glycol, but it should be understood that glycol is only one exemplary desiccant fluid that may be used with such a system. The glycol essentially absorbs the water and other liquids from the natural gas, after which, natural gas is removed from the dehydration system to be sold and the “wet” glycol is cycled through the system to be regenerated or returned to a “dry” state in which it can be reused to dehydrate more natural gas.
The water and other liquids absorbed by the desiccant often include an amount of off-gases containing contaminants such as volatile organic compounds, known in the art as VOC's, and/or aromatic hydrocarbons, known in the art as BTEX. Such off-gases may be in a gaseous state suspended in the water or other liquids, or may be in liquid state, depending upon temperature, pressure, and/or other conditions. These off-gases are generally pollutants which should not be, and in many cases, may not legally be, released into the environment. These off-gases are generally flammable as well.
A number of attempts have been made to find methods for storing and disposing of such off-gases to prevent them from contaminating the environment. Storage methods may involve routing the off-gases to a tank where they can be held for later disposal. Well sites are often in remote locations, however, where it can be difficult, time-consuming, and expensive to periodically retrieve the off-gases for disposal. Additionally, storage tanks may corrode and begin to leak over time.
Disposal methods have included flares and flare stacks to burn the off-gases, reducing them to combustion byproducts that can more safely be released into the atmosphere. Problems remain, however, for such flares and flare-stacks. For example, rates of off-gas removal from natural gas may vary over time as natural gas of varying composition is removed from a well. These variations can result in unpredictable and inconsistent performance of a flare or flare stack, especially those with burners or burner assemblies having valves with fixed flow rates. Additionally, in locations subject to extreme cold, liquids may condense out of the off-gases before reaching the burner of the flare or flare stack. This condensation may cause blockages in fuel lines or permit high-concentrations of combustible materials which may cause explosions that can endanger people, wildlife, and equipment. Additionally, combustion of the off-gases generates thermal energy which is wasted when not put to use.
To this end, a need exists for a dependable flare stack which pre-heats the off-gases before they reach the burner or burner assembly and which harnesses or makes use of the thermal energy created by the combustion of the off-gases. It is to such a flare stack that the present invention is directed.